Printing presses such as lithographic offset presses ofter have a plurality of printing units which may be used for printing a plurality of colors on paper or other stock. An ink fountain for a printing unit of such a press typically includes a source of ink and a number of inking rolls extending across the width of the printing press transversely to the direction of travel of the stock to be printed. The rate of flow of ink from the ink fountain toward the stock is controlled at many locations across the width of the ink fountain in order to produce uniformly dense printed images across the width of the stock. It is not uncommon for each ink fountain to have as many as 64 such locations across its width, at which the rate of ink flow can be individually adjusted by 64 movable members. The movable members, which in one type of ink fountain are ink adjustment keys having screw threads, are adjustable by separate actuators which include bidirectional electric motors.
In one ink fountain of the prior art, each of the ink key actuators is arranged to be driven by two triac semiconductors, one for each rotational direction of the ink key. For remotely controlling the ink fountains of all of the printing units of a printing press, a remote control station was provided at an inspection table at a distance from the printing press. An individual control wire was brought out from a gate electrode of each of the triac semiconductors and connected at its other end to control devices at the remote control station. This control wiring scheme could be classed as "parallel" control because of the arrangement of similar control circuits that were connected between the remote control station and the printing press. Such a "parallel" control system results in duplication of circuits and duplication of cabling, which entails a great amount of equipment when a great number of ink key actuators on a multiple unit printing press are to be controlled.
Some ink fountain control apparatus of the prior art had provision for controlling only one printing unit at a time from the remote control station and had further provision for using that one set of controls in common for all of the printing units by switchably multiplexing the controls to operate a selected one of the printing units. The multiplexing was accomplished by switching the available controls to a selected set of the "parallel" control wires described above. Thus, some control systems of the prior art have succeeded in multiplexing the remote control devices but not the interconnecting cable extending between the remote control station and the printing press.